;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-intermediate-lambda-reader.ss" "lang")((modname foldrr) (read-case-sensitive #t) (teachpacks ((lib "docs.rkt" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "docs.rkt" "teachpack" "htdp")) #f)))
(define (foldrr op ys id)
  (if (null? ys) id
      (op (car ys)(foldrr op (cdr ys) id))))

(foldrr append '((1 2) (3 4)) '()) ; returns (list 1 2 3 4)

(define (len z) (foldrr (lambda (x y) (+ 1 y)) z  0))
(len '(5 6 7))       ; returns 3
(len '(5 (6) ((7)))) ; returns 3

(foldrr + '(1 2 3 4 5) 0) ; returns 15
(foldrr * '(1 2 3) 1)     ; returns 6

(map abs '(-1 2 -3))   ; returns (list 1 2 3)

(define (foldll g ys u) (if (null? ys) u (foldll g (cdr ys) (g u (car ys)))))
(foldll + '(1 2 3 4 5) 0) ;  return 15 but computes it differently than foldrr